Cannot mix .user and .addon keyconfigs in register()
OR use .active without it telling me 'Mesh' keymap doesn't exist


Have you tried checking for and adding it if necessary?

kc=bpy.context.window_manager.keyconfigs.active
km='Mesh' in kc.keymaps and kc.keymaps['Mesh'] or kc.keymaps.new('Mesh')